We have isolated a growth-producing serum tripeptide from human plasma and serum with the structure H-Gly-His-Lys-OH (GHL). Synthetic GHL has activity comparable to the native factor. Nanomolar concentrations of GHL stimulate the growth in culture of a hepatoma (HTC4) cell line and the survival of normal cultured hepatocytes. Recent work has shown GHL to be a chelator of transition metals such as Fe2ion, Cu2ion, Zn2ion, and Co2ion but not of metals such as Ca2ion, Mg2ion, Mn2ion. The combination of these transition metals and GHL in culture medium synergistically enhances cellular attachment to the monolayer support when cells are cultured under minimal growth (low serum) conditions. We propose to study the effects of interaction of GHL and transition metals on: (1) cellular adhesion (to plastic monolayers, cell-to-cell, and to fibrin strands); and (2) other parameters of cell function (growth, macromolecular and lipid synthesis and lactic acid production). Radiolabelled GHL will be used to measure tripeptide binding and uptake by cells, catabolism in cell culture and intact animals, to determine blood concentrations by isotope dilution, and to improve methods of extraction of GHL from body fluids and tissues. Analogs of GHL will be synthesized and their relative activity in cell cultures tested. Correlations between the structure of GHL and its analogs and their tissue-specific effects on growth may provide information useful for eventual synthesis of growth-modulating drugs with potential applications in therapy of neoplastic diseases. Chelation constants between GHL and its analogs, and those transition metals found to interact with GHL in cell culture, will be determined. Studies of the relation between parameters and biological effects of peptide-metal complexes may then be possible.